4.16.24 21st Century Movements for Black Lives.pptx
Fluid Mosaic Model Cell Membrane Structure
1. Fluid Mosaic Model
of The Structure of
Cell Membrane
Wenny Pintalitna Tarigan
Pend.Biologi
2013
2. Background
Biological membranes play a crucial role
in almost all cellular phenomena
Organization of proteins and lipids of
membranes can be discerned
Generalizations about protein structure –
understanding the properties and
functions of protein molecules
Detailed structure
3. Objectives
Thermodynamics and Membrane Structure
Properties of proteins and lipids of functional
membrane
The fluid mosaic model in detail
Experimental evidence in terms of the model
The fluid mosaic model suggests new ways of
thinking about membrane functions and
membrane phenomena
4. Thermodynamics and
Membrane Structure
Two kinds of non covalent
interactions are hydrophobic and
hydrophilic
Hydrophybic – non polar groups,
away from water, requires energy
Hydrophylic – polar groups for
aqueous environment
5. Thermodynamics and
Membrane Structure
Ratio of proteins to lipids = 1.5 – 4
Cell membrane recognition sites
activate enzyme in membrane
which begins "cascade" of events
which activate other enzymes. This
is called signal transduction
(pg 155 Campbell)
6. Properties of Proteins
Peripheral Proteins
- mild treatment: increase the ionic strength -
dissociate them intact from the membrane
- weak non covalent – not strongly associated
with membrane lipid (free of lipid)
- spread out as monolayer
Integral/Transmembrane Proteins
- drastric treatment (using many reagents)
- remain associated with lipid
- globular in shape, no on the surface – prevent
membrane thickness larger than 75-90 A
7. Classes of amino acids
What do these amino acids have in common?
nonpolar & hydrophobic
8. Classes of amino acids
What do these amino acids have in common?
polar & hydrophilic
9. Proteins domains anchor molecule
Within membrane
nonpolar amino acids
hydrophobic
anchors protein
into membrane
On outer surfaces of
membrane
polar amino acids
hydrophilic
extend into extracellular
fluid & into cytosol
Polar areas
of protein
Nonpolar areas of protein
Properties of Proteins
13. Many Functions of Membrane Proteins
Outside
Plasma
membrane
Inside
Transporter Cell surface
receptor
Enzyme
activity
Cell surface
identity marker
Attachment to the
cytoskeleton
Cell adhesion
14. Stronger electron microscopes would show that the
cell membrane was not covered in protein, but
rather had protein embedded in it.
Proteins Embedded on
Cell Membrane
15. Knife
Plasma membrane Cytoplasmic layer
Proteins
Extracellular
layer
Inside of extracellular layer Inside of cytoplasmic layer
TECHNIQUE
RESULTS
Properties of Lipid
16. Membrane phospholipids
form a bilayer
Phospholipids
Have a hydrophilic head
and two hydrophobic tails
Are the main structural
components of membranes
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH3
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH3
CH2
CH2
CH3
CH3
CH3
N
+
O
O O–P
O
CH2
C
H
CH2
C O C O
O O
Phosphate
group
Symbol
Hydrophilic head
Hydrophobic tails
Properties of Lipid
21. FUNCTIONS:
Cell protection and/or insulation
Receptor sites for binding of other molecules - signaling
Attachment of cells to one another = tissues
Carbohydrate Chains – Cell ID – autoimmunity
Carbohydrate
24. Membrane is a collage of proteins & other molecules
embedded in the fluid matrix of the lipid bilayer
Extracellular fluid
Cholesterol
Cytoplasm
Glycolipid
Transmembrane
proteins
Filaments of
cytoskeleton
Peripheral
protein
Glycoprotein
Phospholipids
25. Membrane fat composition varies
Fat composition affects flexibility
membrane must be fluid & flexible
about as fluid as thick salad oil
% unsaturated fatty acids in phospholipids
keep membrane less viscous
cold-adapted organisms, like winter wheat
increase % in autumn
cholesterol in membrane
Fluid Mosaic Model
26. Permeability to
polar molecules?
Membrane becomes semi-permeable via protein
channels
specific channels allow specific material across cell
membrane
outside cell
inside cell sugaraaH2O
saltNH3
27. Experimental Evidence
Integral protein - a globular molecule - embedded in the
membrane.
In this technique, a frozen specimen is fractured with a
microtome knife; some of the frozen water is sub-limed
(etched) from the fractured surface if desired;
The surface is then shadow cast with metal, and the
surface replica is examined in the electron microscope.
By this method the topography of the cleaved surface is
revealed.
A characteristic feature of the exposed surface of most
functional membranes examined by this technique,
including plasma lemma, vacuolar, nuclear, chloroplast,
mitochondrial, and bacterial membranes, is a mosaic-like
structure consisting of a smooth matrix interrupted by a
large number of particles.
28. New Ways of Thinking
Model restrictions imposed by thermodynamics. In this
model, the proteins that are integral to the membrane
are a heterogeneous set of globular molecules
(amphipathic structure)
The bulk of the phospholipid is organized as a fluid
bilayer, although a small fraction of the lipid may
interact specifically with the membrane proteins.
The fluid mosaic structure is therefore formally
analogous to a two-dimensional oriented solution of
integral proteins (or lipoproteins) in the viscous
phospholipid bilayer solvent.
Evidence stated that all of which are consistent with,
and add much detail to, the fluid mosaic model.
Cascade = menyatukanMatriks phospholipid terdiriatasdualapisan, dandidalamnyaterdapatduatipe protein, ialah protein periferyang dapatbereaksidandapatlarutpada air (polar), dan protein integral yang sukarberikatandansukarlarut air (nonpolar)